1. Field of the Invention
The present invention relates to a steering assemblies for bicycles and similar vehicles of the type having a threadless steerer tube and a threadless headset for connecting the steerer tube to the bicycle frame head tube.
2. Description of Related Art
Historically, the stem connecting the handlebars to the steerer tube of a bicycle was of a general “L” shape with one portion extending into the top of the steerer. This portion could be inserted to a varying extent to adjust the height of the handlebars. This historical “L” type stem is used exclusively with steerers having threaded outer diameters. The system allowed for continuous variable adjustment of the handlebar height, but the had many limitations and problems.
With the invention of a headset assembly for bicycles as discussed in U.S. Pat. No. 5,095,770, which allowed the use of a threadless steerer and a simplified stem design, the most commonly used stems offer no height adjustment. To compensate for the lack of adjustability within the stem itself, simple hollow and generally cylindrical spacers have been used above the headset assembly and below the handlebar stems, while the steerers are cut to length once the appropriate height has been determined. These simple hollow cylindrical spacers are used in varying quantities and with varying heights, though typically multiple spacers are used in a stacked arrangement. In some cases, spacers are also placed above the handlebar stem so as to eliminate the need to cut the steerer, thereby enabling the handlebar stem to be raised at a later time.
The currently used simple hollow cylindrical headset spacers have limitations. They must have an inner diameter sufficiently large to enable easy assembly over steerers. Since steerers vary slightly in outer diameter between manufacturers and as a result of normal manufacturing variation of steerers and spacers, there usually exists an undesirable radial clearance between the outer diameter of the steerer and the inner diameter of the spacers.
As a result of radial loads acting on the steerer and emanating from the handlebars, this radial clearance can promote intermittent bending flexure of the steerer between the handlebar stem and the headset assembly and radial movement of headset spacers. These, in turn, cause eccentric loading of the headset bearings, axial movement of the handlebar stem along the steerer, loosening of the headset assembly preload, and noise due to the relative motion between these parts.
Certain newer bicycle forks with steerers made of lightweight composite materials are even more susceptible to these problems. This is likely due to reduced bending stiffness and a lower coefficient of friction between the handlebar stem and steerer. Certain manufacturers even recommend the use of minimal headset spacers to minimize the problems with these forks.
Another limitation of current headset spacers is that there is no provision for preventing rotational motion of headset spacers relative to each other and/or the bottom of the handlebar stem and the top of the headset assembly. Rotational freedom can potentially promote relaxation of the headset preload as well.
Separate and apart from the above-described spacers, are constructions designed to enable the pre-load on the headset bearing assembly to be adjusted after setup of the steerer assembly. One such arrangement is described in U.S. Pat. No. 5,540,457. In this arrangement, the handlebar stem has a tube which fits over the steerer tube and is threaded at its lower end to receive a threaded locking collar. The pre-load on the bearings can be adjusted by turning the locking collar. However, such a pre-load adjustment arrangement is not a substitute for the height adjustment provided by above-described spacers.